Ordinary power supply systems are three-phase systems. However, there are many single-phase loads in practice, especially for traction power supply systems and industrial electricity. The electric railway uses single-phase power frequency AC system, wherein the traction power supply system is connected to the electricity system through the traction substation, and the core equipment of the traction substation is the traction transformer. In recent years, a three-phase to two-phase transformation is applied to the traction transformer of Vv wiring in a direct supply style, the traction transformer of Vx wiring in an AT-style, Ynvd traction transformer, and Scott traction transformer etc., but the traction power supply system still has two essential problems: phase separation problem and negative sequence problem. The problem of phase separation creates a dead zone for the power supply lines. The dead zone significantly affects the overall performance of the traction power supply system. The traction load belonging to a single-phase load is extremely asymmetric, so that a large amount of negative sequence current is introduced into the electricity system, and an extreme imbalance is caused to the three-phase power grid. Moreover, when the locomotive operates with the emergency brakes, the energy generated thereby cannot be returned to the power grid, and only resistors are used to consume the redundant energy, which wastes energy. For the industrial power supply and distribution system, after receiving high voltage, it is subjected to the total step-down substation and the distribution substation. After that, each plant substation takes a certain phase from the three-phase power of the substation. Power supply system needs to go through a plurality of substations, so the process is repetitive and complex. The power frequency transformers in the substation have a large size and weight. Moreover, since the loads of the power frequency transformers are single-phased, both a sudden increase and a sudden reduction will cause the above-mentioned adverse phenomenon.
In view of the drawbacks of the prior art, and in order to solve above problems, a power electronic voltage transforming apparatus, which mainly converts the three-phase power and two-phase power into a single-phase power, is provided. By using the apparatus, the dynamic compensation of negative sequence and reactive power can be realized; the harmonic wave of the single-phase load can be controlled, and the quality of electric energy in the power supply section can be improved. Furthermore, passing the phase separation of the existing traction power supply system can be avoided to achieve energy feedback, etc. The apparatus contributes to the development of high-speed and heavy-load railway. Furthermore, the power frequency transformers of the substations in the industrial power supply and distribution system can be removed to save the land usage.